This grant request funds for the purchase of a flow cytometer. Seven Core Users with current NIH grant support have been identified at Iowa State University (ISU). In addition, eight Potential Users, supported by federal, state, local, and private agencies, are located at ISU. The Core Users propose to use the flow cytometer 75% of the time and the Potential Users will share the remaining 25% of the available time on the instrument. The flow cytometer will be a true university-wide facility, with users from three colleges (Sciences and Humanities, Agriculture, and Veterinary Medicine) and six different departments (Biochemistry and Biophysics, Veterinary Anatomy, Veterinary Microbiology, Genetics, Animal Science, and Zoology). The flow cytometer will be located in the Department of Biochemistry and Biophysics, Room 355J Gilman Hall. No flow cytometer exists at ISU. Excellent research in health-related fields depends on modern biological instrumentation. The flow cytometer is a sophisticated instrument that has revolutionized the analysis and separation of cells and subcellular particles. The availability of this instrument on our campus will improve our efficiency of research and make many experiments possible which cannot presently be undertaken. The major areas of research to be investigated are: (1) role of the major histocompatibility complex in development and aging; (2) functional heterogeneity of prolactin-secreting cells; (3) mechanism of action of steroids on the differentiation of the preoptic area of the brain; (4) structure and function of a secreted protein induced by a growth inhibitor; (5) role of histocompatibility immune response genes in disease resistance in the chicken; (6) control of the metabolism and storage of vitamin A in the liver and in selected tumor cells; and (7) biological significance of LPS from Bacteroides fragilis.